Porous nickel bodies are difficult to satisfactorily interiorly silverplate. The problem intensifies with increasing diminishment of the void spaces involved, about which the plating deposit is desired to be made on the enclosing wall surfaces thereof. This is particularly so in cases where the body to be interiorly plated is a porous electrode intended for usage electrochemically. Characteristically, these contain an abundance of exceedingly fine, internal body-traversing pores which oftentimes are of minuscule size on the order of 10-25 microns and less to as small as even 0.1 micron or so.
Attempts to overcome the mentioned difficulty have not met with general success nor have they been without certain inherently unattractive features and limitations.
For example, U.S. Pat. No. 3,539,469 discloses a replacement plating process for acid treated nickel powders to be subsequently fabricated into electrode bodies for fuel cells and so forth. However, the therein taught technique neither contemplates nor includes plating of fabricated porous bodies and, in addition, requires application of considerable, relatively costly quantities of silver for the plating of the particles on the usual order of from 10-30 weight percent.
U.S. Pat. No. 3,787,244 involves use of a single, one-stage application acid/noble metal salt solution for catalytic plating of various porous metal electrode bodies, including those of nickel. Such a reagent is generally inoperable for silver plating purposes due to involved insolubility problems with the silver salts in the highly acidic (i.e., pH 0.5-2), simultaneously dual-functioning solutions employed.